The present invention relates to a vibration damper, for damping rotating masses, and includes a primary part that is adapted to be mounted on a shaft, especially a crankshaft of a multi-cylinder reciprocating-piston internal combustion engine, and a secondary part that is disposed in the radial direction relative to the primary part and is connected to the latter via an elastic damping means, preferably of rubber, with a support element for a V-belt pulley furthermore being secured to the primary part.
A torsional vibration damper of this general type was disclosed in German Offenlegungsschrift No. 27 44 406.
Dampers of this type start to operate only when resonance speeds occur, with the vibration system being split by the elastic connection of the secondary part into an additional form of vibration with nodes in the damper. By appropriate tuning, it is possible to damp dangerous resonances effectively.
The end of the cranksaft on which the torsional vibration damper is mounted (opposite the flywheel end) is at the same time preferably used to drive auxiliary devices and for other power take-off. In this connection, reference is made to "Front power take-off", abbreviated "Front PTO". Appropriate variants of V-belt pulleys, referred to as "fan-end mass moments of inertia", are provided on the primary or secondary end of the damper.
If a given spring-mass system is provided with a different fan-end moment of mass inertia, in most cases that involves a readjustment of the damper, i.e. corresponding moments of mass inertia at the fan end require specific dampers with associated characteristic frequencies. In this case it is customary to adapt the characteristic frequency to the "engine crankshaft" vibration system.
The substantial change in the vibration behavior is due to the fact that on account of their greater distance from the vibration node, the fan-end masses have a greater effect upon the frequency behavior than do corresponding masses (for example from a coupling) at the flywheel end.
It has also been possible to establish by means of measurements that, apart from the influence of masses of inertia, influence is also exerted by the torque transmission. It has thus been possible to observe that in the case of radial power take-off via V-belts, negative changes have occurred in the damper stressing, depending upon the power take-off.
As a result of the above-mentioned adjustment of the characteristic frequency, the first "Front PTO" vibration system, i.e. the attached operating machines or auxiliary drive, considered in terms of torsional vibration, was frequently driven in the subcritical range (i.e. the excitation frequency is below the natural frequency), and in part even in resonance. In this connection it is necessary to mention the disadvantage that continuing or extending structural elements of the PTO are subjected to increased stressing due to rotational angle deflections and vibration moments. Increased noise, e.g. in power-drive transmissions, and increased wear of the components on shaft hub connections and universal-joint shafts, result in part in unsatisfactory operating results.
The object of the present invention is to keep a vibration damper of the aforementioned general type as free as possible from the effects of the PTO, and to embody the PTO in such a way that the latter is more suitable for the fluctuating power requirement that occurs there in the case of radial and/or axial power take-off, i.e. that the PTO is properly insulated against vibration and is free from noise.